Activation energy radiation chemical yield

The most characteristic type of primary activations are the electronic transitions of molecules which are much faster than other response of the irradiated medium. This enables one to consider separately the physical stage of radiolysis, at the end of which a certain ensemble of excited and ionized molecules is formed in the medium. Each of the activated molecules possesses a particular amount of energy available for subsequent processes. The initial distribution and yields of individual primary activations are dealt with by the theory of primary radiation chemical yield (PRCY). We have studied the application of this theory to the radiolysis of gases in detail during the last years (16, 17, 18, 19, 20). Thus, in the formal expression—see (5), for the yield G(X) = %ngncompetitive reaction ways and remain much more obscure at the present. 

In the CM-chitosan solutions that contained 0.02mol/L H2O2 (condition c) or 2.5 x 10" mol/L N2O (condition b), were 280% and 150% of that in condition a (Nj-saturated). In condition d, because 0.76 mol/L isopropanol was added into the CM-chitosan solution, G decreased to 5% of that in condition a. Similar to the degradation mechanism of chitosan in aqueous solution, the radiation energy of y-ray is absorbed mainly by water in dilute CM-chitosan aqueous solutions, and the direct effect of radiation on CM-chitosan can be neglected. The radiation chemical yield of reactive species released in the radiolysis of water are constant in the wide range of pH. In condition a, CM-chitosan aqueous solution was radiated with saturated N2. The active species that resulted in... 

The ultimate loss of the HAS activity occurs by destruction of the heterocycle initiated thermally, photochemically, chemically or by high-energy radiation. An intramolecular H-abstraction from the p-carbon atom in thermolysis of 2,2,6,6-tetramethyl-4-oxo-piperidinyl-l-oxyl 133 via a general reaction (Eq. 8) was proposed as a pathway of thermal selfdestruction of the piperidine cycle [25] (Scheme 25). The respective hydroxylamine was isolated in the yield of 66.5%. The biradical intermediate 137 either dimerizes to nitroxide 138 or thermolyses via 139 to a nitrogen-free fragment 140 (phorone) and nitric oxide. 

For near and supercritical conditions, combustion gas-phase data are often used as the point of reference to assess solvent effects. The gas-phase values of kig, available for temperatures 800-2500 K, show the activation energy 90 kJ mol In condensed phase, stabilization of H2O molecules via H-bonding may increase the activation barrier, but on the other hand the reaction can be promoted by the solvent cage effect. Diffusion-kinetic modelling and stochastic simulation of chemical reactions in radiation tracks have shown that the occurrence of reaction (15.19) is consistent with the anomalous increase in H2 yield observed in water radiolysis at temperatures above 523 K, if kig is of the order of 1-2x10 s (4-8x10 s ) at 573 K. Considering the two... 

The actual value of the quantum yield provides information that makes it possible to understand the nature and the importance of the secondary processes. When 4> < 1, a part of the energy of the excited or activated molecules is lost (by transformation to thermal energy, for example) before they can react chemically or products of the primary process are formed in secondary processes. When > 1, chain reactions are initiated by the reacting molecules. Activation of molecules depends on the radiation intensity, on its wavelength, and on polymer chemical structure but not on the total quantity of energy absorbed from the radiation. 

The law of photochemical equivalence is restricted to primary photochemical process, i.e., each reacting species excited by the absorption of one radiation get chemicd transformation and formed products produce no further reaction. In such cases, these will be 1 1 relationship between the number of quantas absorbed and the number of reacting molecules. But in practice, most of photochemical reactions undergoes secondary photochemical reactions, i.e., photochemically activated species or product molecule initiates a series of chemical transformations while in some cases, photochemically activated species undergoes deactivation, they lose their energy in the form of heat or radiation. Under such conditions, there will be no more 1 1 relationship between the number of quanta absorbed and the product molecules. The deviation from photochemical equivalence (1 1 relationship) is described by the idea of quantum yield or quantum efficiency (< )). It is defined as... 

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